Also appears in collection : 2019 - T3 - WS1 - Nonlinear and stochastic methods in climate and geophysical fluid dynamics

Turbulent flows are characterized by a self-similar energy spectrum, signature of fluid movements at all scales. This organization has been described for more than 70 years by the phenomenology of "Kolmogorov cascade": the energy injected on a large scale by the work of the force that moves the fluid (e. g. a turbine) is transferred to smaller and smaller scales with a constant dissipation rate, up to the Kolmogorov scale, where it is transformed into heat and dissipated by viscosity.

I will explain why this image, which Landau questioned in the 1950s, is false. I will use recent velocity measurements obtained by very high resolution laser velocimetry to show that the energy "cascade" is in fact driven by extreme events on a very small scale, which are the signature of quasi-singularities of the Navier-Stokes equations existing under the Kolmogorov scale.